1. Technical Field
The present invention relates to an ultrasonic obstacle detector for detecting an obstacle using an ultrasonic sensor that transmits and receives ultrasonic waves.
2. Background Art
A conventional obstacle detector for vehicles is shown in the Japanese Patent Publication (unexamined) No. 27779/1988. This detector is provided with an ultrasonic horn, and extraneous matter such as snow or mud is detected by an ultrasonic microphone disposed near an opening of the horn or an electrode disposed in the horn each serving as means for detecting the extraneous matter stuck to the horn.
Since the conventional ultrasonic obstacle detector is constructed as described above, it is necessary to add any assistant parts such as additional ultrasonic microphone or electrode in the horn in order to detect the extraneous matter such as snow or mud.
The present invention was made to resolve the above-discussed problems and has an object of providing an ultrasonic obstacle detector capable of easily detecting foreign matter without additional parts to the ultrasonic sensor.
An ultrasonic obstacle detector according to Embodiment 1 of the invention is an ultrasonic obstacle detector for detecting an obstacle using at least one ultrasonic sensor transmitting and receiving ultrasonic waves comprising;
a plurality of ultrasonic sensors disposed close to each other so that one of the ultrasonic sensors is arranged to. receive direct waves transmitted from at least one of the other ultrasonic sensors, and
means for detecting a state of extraneous matter such as snow or mud sticking to the mentioned ultrasonic sensors according to reception level of the mentioned direct waves.
An ultrasonic obstacle detector according to Embodiment 2 of the invention is an ultrasonic obstacle detector for detecting an obstacle using at least one ultrasonic sensor transmitting and receiving ultrasonic waves comprising;
not less than three ultrasonic sensors disposed close to each other so that one of the ultrasonic sensors is arranged to receive direct waves transmitted from at least one of the other ultrasonic sensors, and
means for judging the ultrasonic sensors to which extraneous matter such as snow or mud is sticking according to reception level of the direct waves for each combination of an ultrasonic sensor transmitting ultrasonic waves and an ultrasonic sensor receiving the transmitted direct waves, the combination being changed in order.
An ultrasonic obstacle detector according to Embodiment 3 of the invention is an ultrasonic obstacle detector for detecting an obstacle using at least one ultrasonic sensor transmitting and receiving ultrasonic waves comprising;
a plurality of ultrasonic sensors disposed close to each other so that one of the ultrasonic sensors is arranged to receive direct waves transmitted from at least one of the other ultrasonic sensors, and
means for calculating a temperature on the basis of a transfer time and a transfer distance of the mentioned direct waves between the two ultrasonic sensors transmitting and receiving the direct waves, and judging whether or not there is a possibility of snow, frozen ice, or the like sticking to the mentioned ultrasonic sensors according to a value of the calculated temperature.
In the ultrasonic obstacle detector as set forth in claims 1 to 3 of the invention, whether or not extraneous matter such as snow or mud is sticking onto the ultrasonic sensors is detected by monitoring direct waves from the ultrasonic sensors.